Cathode ray tube comprising at least one electron gun for producing a number of electron beams

ABSTRACT

A cathode ray tube, in particular a color tube, in which two or more electron beams are produced, focused, and converged on a picture display screen. A part of each electron beam is intercepted and reflected against a given part of the neck as a result of which the potential thereof rapidly adjusts at an equilibrium value after switching on the tube.

United States Patent Peper [4 1 May 22,1973

C ATHODE RAY TUBE COMPRISING AT LEAST ONE ELECTRON GUN FOR PRODUCING A NUMBER OF ELECTRON BEAMS Inventor: Jan Peper, Emmasingel, Eindhoven,

Netherlands U.S. Philips Corporation, New York, NY.

Filed: Mar. 1, 1972 Appl. No.: 230,762

Assignee:

Foreign Application Priority Data Mar. 16, 1971 Netherlands ..7103464 U.S. Cl. ..3l3/70, 313/75, 313/83 Int. Cl .1101] 29/56 Field of Search ..3 13/70, 75, 83

[56] References Cited UNITED STATES PATENTS 3,517,242 6/1970 Pappadis..........................i..313/70C 3,560,779 2/1971 May ..3l3/7O Primary Examiner-John Kominski AttorneyFrank R. Trifari 57 ABSTRACT A cathode ray tube, in particular a color tube, in which two or more electron beams are produced, focused, and converged on a picture display screen. A part of each electron beam is intercepted and reflected against a given part of the neck as a result of which the potential thereof rapidly adjusts at an equilibrium value after switching on the tube.

4 Claims, 3 Drawing Figures CATIIODE RAY TUBE COMPRISING AT LEAST ONE ELECTRON GUN FOR PRODUCING A NUMBER OF ELECTRON BEAMS The invention relates to a device including a cathode ray tube which comprises within a glass envelope an electron gun system for producing and focusing two or more electron beams which are converged in a given plane, and including a picture display screen. The picture display screen in such a cathode ray tube comprises, for example, a number of different luminescent materials and a color selection electrode is placed at a short distance from the picture display screen, a number of electron beams corresponding to the number of luminescent materials being produced by the electron gun system. These beams are then converged in the plane of the color selection electrode.

In the said cathode ray tube, each of the electron beams is focused on the picture display screen or at least on a surface situated near said screen, for example that of the color selection electrode in the case of a color tube. This occurs mainly by the lens effect between successive electrodes of the gun or guns which constitute the electron gun system, converging of the electron beams occurs either magnetically or electrostatically. Since the successive electrode of the gun or of the guns do not screen the electron beams entirely relative to the wall of the glass envelope at the area, electric charges on the walls influence the focusing and the converging. This influence is best noticeable in converging the electron beams; in the case of the color tube they are no longer converged in the plane of the color selection electrode. It is possible for a given value of the potential of the glass surface around the electron gun system to adjust the magnetic or electrostatic convergence in such manner that the electron beams are converged in the relevant plane. However, a difficulty presents itself in the time that the potential of the glass surface has not yet reached the equilibrium value, during which period the convergence is not good and the electron spots on the picture display screen move relative to each other; in the case of the color tube, the frames in the various colors shift relative to each other in this period. This manifests itself in particular upon adjusting the convergence device because one has each time to wait until the equilibrium value is reached, which means a loss of time during manufacture.

From US. Pat. No. 3,517,242 a cathode ray tube is known for displaying color pictures which comprises more than one electron gun. In order to reduce the above-mentioned convergence drift after switching on the tube, an electron of at least one of the electron guns situated between the cathode and the anode of the electron gun in question is connected mechanically and electrically to the glass wall by means of a conductive contact. A difficulty which presents itself is that in connection with the poor electric conductivity of the glass, a certain potential is always present on the wall only at the area of the contact, which, however, does not hold good for the further part of the circumference of the glass wall at that area.

The invention is based on the recognition of the fact that it is important that the potential of the glass surface around the electron gun system adjusts at the equilibrium value as quickly as possible upon switching on the tube. This equilibrium value is determined for the greater part by the configuration of the electron gun system. The leak of electric charge along the glass wall may be neglected in practice. The speed at which the equilibrium condition of the potential of the glass surface adjusts, depends upon the number of electrons which impinge upon the glass surface around the electron gun system per unit of time and upon the secondary emission coefficient of the glass surface. It is therefore of importance to increase the number of electrons which impinge upon the glass surface, as a result of which the equilibrium condition adjusts more rapidly.

According to the invention, a part of each electron beam is intercepted and reflected by an electrode of the electron gun system in such manner that reflected electrons impinge upon the glass surface at the area of an aperture between two electrodes situated farther from the picture display screen. In particular, a part of each electron beam is intercepted by the last electrode of the electron gun system and reflected electrons impinge upon the glass surface at the area of the aperture between the penultimate electrode and the last electrode. The penultimate electrode is sometimes termed focusing anode and the last electrode is termed final anode.

Intercepting of a part of an electron beam can be car ried out in various manners. For that purpose, for example, the aperture in an electrode is smaller than the diameter of the electron beam, or said aperture is substantially equal to the diameter of the electron beam but the center of the aperture is situated eccentrically relative to the axis of the beam. In still another construction, electrons are intercepted in the aperture by one or more projections of the electrode, or the aperture is closed by a gauze having a rather large transmis sion, or a wire is stretched across the aperture in the path of the electron beam. A part of the intercepted and reflected electrons are reflected by the field between the electrodes in the direction of the glass surface around the electron gun system and they bring said glass surface rapidly at its equilibrium potential. In a particularly favorable embodiment a gauze having a high transmission and a freely permeable part for the center of the beam is present in the last electrode of each electron gun in a plane at right angles to the axis at least at the part situated near the circumference. This gauze may be situated at the end of said last electrode facing the screen where it passes into the convergence device which is common for all the guns.

In order that the invention may be readily carried into effect it will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which FIG. I is a sectional view of a cathode ray tube,

FIG. 2 shows a neck of the cathode ray tube partly broken away,

FIG. 3 is a perspective illustrating, partly broken away, of the last electrode of the gun shown in FIG. 2.

Referring now to FIG. 1, a cathode ray tube I comprises a diagrammatically shown system of guns 2 which has three guns and an internal convergence device. The guns are arranged in a triangular position and each produces an electron beam; the electron beams are converged on a shadow mask 4 by a convergence device consisting of an internal convergence device associated with the system of guns 2 and a diagrammatically shown external convergence device 3, after which they each impinge upon distinct parts of a luminescent screen 5. The scanning of the screen is effected by a diagrammatically shown deflection device 6.

in HQ. 2 is shown the neck 7 of the cathode-ray tube partly broken away, as a result of which one of the guns is Vllsthit'i. This gun comprises the following components which are shown slightly diagrammatically, the mechanical connection and electron connection being not shown: a cathode 8, a substantially plate-shaped first grid 9, a substantially plate-shaped second grid 10, a tube-like third grid 11 and a tube-like fourth grid 12, which opens into a tube 13 associated with the internal convergence device. The latter tube is closed by a gauze, while apertures are present in a plate-shaped part 14 at right angles to the plane of the drawing which forms the connection between the tube-shaped fourth grid 12 and tube 13.

FIG. 3 shows how an electrode 12 when it passes into the convergence device is closed by a gauze 16. Intersecting tungsten wires of 20 m thickness and a pitch of 200 m are stretched on the aperture in 12 of4 mm diameter. The gauze is welded or soldered by means of gold, the wires touching each other. When an electron beam of high energy is conveyed for the first time through the electrode 12, the center of the beam with its high density will burn a hole 17 in the gauze with a diameter of approximately 0.6 mm. The less dense outer part of the beam is partly reflected by the outer part of the gauze, in which the reflected electrons can be deflected by the field between the electrodes 11 and 12 to the wall of the glass neck 7 approximately at the area 15. With normal beam current in the gun, the equilibrium potential of the wall adjusts within approximately seconds. The advantage of this embodiment is that it is not necessary to accurately center a small aperture, the beam burns the aperture in the gauze in the correct place and the passing beam is influenced as little as possible. The small quantity of evaporated grid wirc need not have any detrimental effects.

During operation of the tube a part of the electrons intercepted by the gauze 16 is reflected, passes through the apertures in the plate-shaped part 14 and impinges upon the glass surface of the neck 7 approximately at the area 15 (H0. 2). As a result of this, the potential of the glass surface around the aperture between the grids 11 and 12 and the apertures between the corresponding grids of the other guns adjusts at an equilibrium value within a short time after switching on the tube.

What is claimed is:

l. A device including a cathode ray tube which comprises within a glass envelope an electron gun system for producing and focusing two or more electron beams which are converged in a given plane, and including a picture display screen, characterized in that a part of each electron beam is intercepted and reflected by an electrode of the electron gun system, all this in such manner that reflected electrons impinge upon the glass surface at the area of an aperture between two electrodes situated farther from the picture display screen causing a relatively rapid adjustment of the said glass surface to a condition of potential equilibrium.

2. A device as claimed in claim 1, characterized in that the last electrode of the electron gun system inter cepts a part of each electron beam and reflected electrons impinge upon the glass surface at the area of the aperture between the penultimate electrode and the last electrode.

3. A device as claimed in claim 1, characterized in that a gauze having a high transmission and a freely permeable part for the center of the beam is present in the last electrode of each electron gun in a plane at right angles to the axis at least at the part near the circumference.

4. A device as claimed in claim 3, characterized in that the gauze is present at the end of the last electrode facing the screen where it passes into a convergence device which is common for all the guns.

* t i ii i 

1. A device including a cathode ray tube which comprises within a glass envelope an electron gun system for producing and focusing two or more electron beams which are converged in a given plane, and including a picture display screen, characterized in that a part of each electron beam is intercepted and reflected by an electrode of the electron gun system, all this in such manner that reflected electrons impinge upon the glass surface at the area of an aperture between two electrodes situated farther from the picture display screen causing a relatively rapid adjustment of the said glass surface to a condition of potential equilibrium.
 2. A device as claimed in claim 1, characterized in that the last electrode of the electron gun system intercepts a part of each electron beam and reflected electrons impinge upon the glass surface at the area of the aperture between the penultimate electrode and the last electrode.
 3. A device as claimed in claim 1, characterized in that a gauze having a high transmission and a freely permeable part for the center of the beam is present in the last electrode of each electron gun in a plane at right angles to the axis at least at the part near the circumference.
 4. A device as claimed in claim 3, characterized in that the gauze is present at the end of the last electrode facing the screen where it passes into a convergence device which is common for all the guns. 